Recently, miniaturization of semiconductor devices is advancing in order to improve performance of the devices. Further, it is required to reduce power consumption of the semiconductor devices due to the effect on the environment or the application to mobile devices. To that end, in a MOSFET, a combination of a metal gate and a high-k film made of a high-k material is introduced. The high-k (high dielectric constant) film is also used for a capacitor unit in order to increase a capacity of a DRAM.
As for the high-k film, a laminated film of oxides such as HfO2 and ZrO2 or Al2O3 and ZrO2 is used. However, in the case of using such an oxide material for the semiconductor devices, an oxygen vacancy may occur in the high-k film. If the oxygen vacancy occurs in the high-k film, a dipole is generated at an interface of the electrode or the metal gate adjacent to the high-k film and a band is bent by the dipole, which leads to a low effective work function. As a result, electrons readily flow and a leakage current is increased.
As for a technique for solving the above drawback, techniques for reducing oxygen vacancy in a high-k film by adding oxygen to a TiN film used as the electrode or the metal gate formed on the high-k film are disclosed in Japanese Patent Application Publication No. 2015-506097 and E. Cartier, et al., Appl. Phys. Lett., Vol. 95, 2009, p. 042901. Specifically, the TiN film is formed by PVD (Physical Vapor Deposition) and, then, oxygen is added to the TiN film by performing oxygen plasma processing or annealing using oxygen-containing gas.
However, as the miniaturization of the semiconductor devices progresses, when a film is formed, a high step coverage is required in a fine pattern and, also, high controllability of a thin film is required. Therefore, when the TiN film is formed, sufficiently high step coverage is not obtained by the PVD and a sufficiently high controllability of the thin film is not obtained even by CVD (Chemical Vapor Deposition) that provides a better step coverage compared to PVD. Further, in the case of the technique disclosed in Japanese Patent Application Publication No. 2015-506097 and E. Cartier, et al., Appl. Phys. Lett., Vol. 95, 2009, p. 042901, the amount of oxygen to be added to the TiN film is limited and, thus, a desired amount of oxygen may not be added.
Therefore, it is examined to form a TiON film by exposing a TiN film to an oxygen plasma or by flowing an oxygen-containing gas at a regular interval during film formation based on a method for forming a TiN film by alternately supplying a TiCl4 gas as a Ti-containing gas and a NH3 gas as a nitriding gas while ensuring an excellent step coverage and high controllability (see, e.g., Japanese Patent Application Publication No. 2003-077864). Accordingly, it is possible to ensure an excellent step coverage and high film formation controllability and also possible to add a sufficient amount of oxygen to the film.
However, it was found that the technique for supplying an oxidizing agent such as an oxygen plasma, an oxygen-containing gas or the like at a regular interval during the TiN film formation by alternate supply of TiCl4 gas and NH3 gas is disadvantageous in that the smoothness of the film becomes poor due to the supply of the oxidizing agent in the initial stage of the film formation.
If the aspect ratio is increased as the miniaturization of the devices progresses, e.g., as an opening of a capacitor structure of a DRAM becomes narrower, reduction of TiCl4 at a bottom (cylinder bottom) of a via may not be sufficient. When the reduction is insufficient, chlorine is separated from TiCl4 by the following reaction (1). However, the nitriding of Ti by the following reaction (2) may not be sufficient.TiCl4+NH3→Ti—+Cl separation  (1)Ti—+NH3→TiN nitriding  (2)
When the reaction (1) occurs but the reaction (2) is insufficient, a dangling bond exists at the TiN film before oxidation. Since the dangling bond is active, it readily reacts with oxygen in the high-k film even during the film formation and, thus, oxygen vacancy occurs in the high-k film. Accordingly, even If the TiON film is formed near the high-k film, it is difficult to sufficiently improve the characteristics of the devices.
Further, it was found that the technique for supplying an oxidizing agent such as an oxygen-containing gas, an oxygen plasma or the like at a regular interval during the film formation performed by alternate supply of TiCl4 gas and NH3 gas has drawbacks in which Cl of about 0.7 at. % remains and smoothness is poor.
In the case of forming a TiON film in a via having a high aspect ratio or the like, it may be difficult for oxygen to reach the bottom of the via. In that case, it is required to increase an oxidizing efficiency.